Medical device for sensing cardiac function

ABSTRACT

A medical device to monitor and treat a patient includes at least one ECG sensing electrode configured to sense a patient ECG signal, a plurality of therapy electrodes configured to deliver one or more therapeutic shocks, and a controller. The controller is configured to select a first ECG template based on a first ECG signal received during a first period of time, select a second ECG template based on determining from a second ECG signal received during a second period of time that the second ECG template represents a better fit, determine whether the patient is experiencing a treatable cardiac event based in part on one or more morphological differences between the second ECG signal and one or more of the first and second ECG template, and cause the medical device to initiate a treatment sequence in response to determining that the patient is experiencing the treatable cardiac event.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 120 as acontinuation of U.S. application Ser. No. 15/081,170, titled “MEDICALDEVICE FOR SENSING CARDIAC FUNCTION,” filed Mar. 25, 2016, which claimspriority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser.No. 62/139,318, titled “MEDICAL DEVICE FOR SENSING CARDIAC FUNCTION,”filed Mar. 27, 2015, each of which is hereby incorporated herein byreference in its entirety.

BACKGROUND Technical Field

This disclosure relates to medical devices, and more particularly tomedical devices that monitor patient cardiac function.

Discussion

Many cardiac patients have conditions which can result in excessivelyfast or erratic heartbeats. If not treated promptly, ventricularfibrillation or certain ventricular tachycardias can result in a fataloutcome. If such arrhythmias are promptly detected and treated, such asby electric shock defibrillation, the result of such an attack can oftenbe minimized Treatment is normally needed within a few minutes of theonset of the condition to be effective. Therefore, it can be critical toaccurately detect such a condition as soon as possible after itsoccurrence.

Ventricular tachycardia and ventricular fibrillation are two heartrhythms that are treatable by an electrical shock properly applied tothe body of the patient. Both of these conditions sometimes occur alongwith a detectable high heart rate in the patient. Utilization of athreshold heart rate will detect these two conditions in many cases andtreatment can begin. Unfortunately, other conditions such as, forexample, supraventricular tachycardia also have a high heart rate andthese are not treatable by electric shock therapy. Therefore, utilizinga detection methodology which relies only on heart rate to institutetreatment may cause treatment to be rendered under conditions whereshock therapy may be inappropriate.

SUMMARY

Some aspects and examples herein accurately identify cardiac eventsexperienced by a patient by comparing the electrocardiogram (ECG) signalof the patient with one or more ECG templates associated with thepatient. For example, medical devices in accord with some examplesgenerate an electrocardiogram (ECG) template for the patient based onrecorded patient ECG information while the patient is not experiencing acardiac condition (e.g., ventricular fibrillation, ventriculartachycardia, or supraventricular tachycardia). The generated ECGtemplate may be compared with the ECG signal of the patient byconstructing a matched filter based on the ECG template and filteringthe patient ECG signal. The output of the matched filter may be acorrelation between the patient ECG signal and the ECG template that maybe analyzed to determine whether the patient is experiencing a cardiaccondition and/or identify a specific type of cardiac condition.

In some examples, the medical device updates the ECG templates asappropriate for the patient. Updating the ECG template may beadvantageous because the sinus rhythm of a patient may change as theactivity levels of a patient change. A patient who has lost weight byexercising may experience a change in normal sinus rhythm. The medicaldevice may update the ECG template, for example, periodically oraperiodically. It is appreciated that the generation of a new ECGtemplate may be triggered by detection of a particular event. Forexample, a user interface of the medical device may permit the patient(or a caretaker of the patient) to initiate various ECG templategeneration processes. The medical device may also detect that adifferent patient is using the medical device and, in response, initiatean ECG template generation process.

According to at least one aspect, a medical device is provided. Themedical device includes at least one electrode to sense anelectrocardiogram (ECG) signal of a patient and a controller coupled tothe at least one electrode. The controller may be configured to generatea first ECG template based on a first ECG signal of the patient,generate a second ECG template based on a second ECG signal of thepatient, and determine whether the patient is experiencing a cardiacevent based on the ECG signal of the patient and an identified one ofthe first ECG template and the second ECG template.

In one example, the ECG signals for use in determining whether thepatient is experiencing a cardiac event can be acquired from real timemonitoring of the patient. In one example, the controller is configuredto perform a convolution operation on the ECG signal and at least one ofthe first and second ECG templates to determine whether one or morecharacteristics of the ECG signal indicate either the presence orabsence of the cardiac event. In one example, at least one of the firstand the second ECG signals are received during operation of a baseliningmode of the medical device. In on example, the ECG signal is receivedduring operation of a monitoring mode of the medical device.

In one example, the controller is configured to compare the second ECGtemplate with the first ECG template to generate a comparison, determinea quality score corresponding to the second ECG template based on thecomparison, and, based on the quality score, identify the second ECGtemplate as the at least one of the first ECG template and the secondECG template for a subsequent determination of whether the patient isexperiencing a cardiac event. In one example, the controller isconfigured to determine whether the patient is experiencing the cardiacevent in part based on one or more morphological differences between theECG signal and one or more of the first and second ECG templates.

In one example, the controller is configured to generate the second ECGtemplate during a second time period that is different from a first timeperiod in which the first ECG template is generated. In this example,the second time period may occur subsequently to the first time periodand the second time period may span a different duration than the firsttime period.

In one example, the controller is configured to generate the second ECGtemplate on a predetermined schedule. In one example, the controller isconfigured to generate the second ECG template during a baseliningoperation initiated by one of a remote server, a human operator, and thepatient. In one example, the controller is configured to provide anotification prior to generating at least one of the first ECG templateand the second ECG template by a baselining operation.

In one example, the controller is configured to generate at least oneECG template of the first and second ECG templates by determiningnumerical coefficients of one or more matched filters based on analysisof an identified ECG signal corresponding to the at least one ECGtemplate. In this example, the controller may be configured to determinewhether the patient is experiencing a cardiac event based in part byfiltering the ECG signal with at least one of the one or more matchedfilters.

In one example, the controller is configured to read a parameter thatspecifies a delay between generation of the first ECG template andgeneration of the second ECG template. In one example, the controller isconfigured to compare the first ECG template to the second ECG templateand to discard the second ECG template responsive the second ECGtemplate deviating from the first ECG template by a thresholdmeasurement. In one example, the controller is configured to associatethe first ECG template with a first patient, associate the second ECGtemplate with a second patient, and to identify the at least one of thefirst ECG template and the second ECG template based on an automaticdetermination of an identity of a patient as either the first or secondpatient from the patient's ECG signal.

In one example, the medical device includes a motion detector to detectand record historical information relating to a patient's movement andthe controller is configured to identify the at least one of the firstECG template and the second ECG template based on the historicalinformation relating to the patient's movement. In this example, thecontroller may be configured to calculate an activity score based on thehistorical information relating to the patient's movement, and toidentify the at least one of the first ECG template and the second ECGtemplate based on the activity score.

In one example, the medical device includes at least one antenna coupledto the controller and the controller is configured to transmit, via theat least one antenna, one or more of the first ECG template and thesecond ECG template to an external system. In one example, the medicaldevice includes at least one antenna coupled to the controller andwherein the controller is configured to receive, from an external systemvia the at least one antenna, one or more of the first ECG template andthe second ECG template.

In one example, the medical device includes at least two electrode pairsand the controller is configured to determine whether the patient isexperiencing the cardiac event by comparing each pair of signals fromthe at least two electrode pairs with either the first ECG template orthe second ECG template using one or more matched filters. In thisexample, the controller is configured to perform a signal operationbased on the one or more matched filters on each pair of signals fromthe at least two electrode pairs and either the first ECG template orthe second ECG template. The signal operation may include, for example,a convolution operation on a pair of signals and either the first ECGtemplate or the second ECG template.

In one example, the controller is configured to determine whether thecardiac event is a treatable arrhythmia or an untreatable arrhythmia byperforming a morphology analysis of the ECG signal with respect to theat least one of the first ECG template and the second ECG template. Thetreatable arrhythmia may include, for example, either ventriculartachycardia or ventricular fibrillation and the untreatable arrhythmiamay include, for example, supraventricular tachycardia. In this example,the morphology analysis may include detecting a QRS complex in the ECGsignal, and where the QRS complex is detected, determining that thecardiac event is an untreatable arrhythmia It is appreciated thatdetecting the QRS complex may include performing a convolution operationon the ECG signal and at least one of the first and second ECG signalsto determine whether one or more characteristics in the ECG signalindicate either presence or absence of the QRS complex.

In one example, the medical device comprises one of a wearabledefibrillator, an in-hospital defibrillator, a mobile cardiac telemetrymonitor, and an automated external defibrillator. In one example, thecardiac event includes at least one of premature ventricular contraction(PVC), ventricular fibrillation (VF), ventricular tachycardia (VT), andsupraventricular tachycardia (SVT).

According to at least one aspect, a medical device is provided. Themedical device includes at least one electrode to sense anelectrocardiogram (ECG) signal of a patient and a detection component.The detection component may be configured to generate a first ECGtemplate based on a first ECG signal of the patient, generate a secondECG template based on a second ECG signal of the patient, and determinewhether the patient is experiencing a cardiac event based on the ECGsignal of the patient and an identified one of the first ECG templateand the second ECG template.

In one example, the ECG signals for use in determining whether thepatient is experiencing a cardiac event can be acquired from real timemonitoring of the patient. In one example, determining whether thepatient is experiencing the cardiac event includes performing aconvolution operation on a signal representation of the ECG signal and acorresponding signal representation of at least one of the first andsecond ECG templates to determine whether one or more characteristics ofthe ECG signal indicate either the presence or absence of the cardiacevent. In one example, at least one of the first and the second ECGsignals are received during operation of a baselining mode of themedical device. In one example, at least the ECG signal is receivedduring operation of a monitoring mode of the medical device.

In one example, the detection component is further configured to comparethe second ECG template with the first ECG template to generate acomparison, determine a quality score corresponding to the second ECGtemplate based on the comparison, and based on the quality score,identify the second ECG template as the at least one of the first ECGtemplate and the second ECG template for a subsequent determination ofwhether the patient is experiencing a cardiac event.

In one example, determining whether the patient is experiencing thecardiac event includes to determine whether the patient is experiencingthe cardiac event in part based on one or more morphological differencesbetween the ECG signal and one or more of the first and second ECGtemplates.

In one example, the second ECG template is generated during a secondtime period that is different from a first time period in which thefirst ECG template is generated. In this example, the second time periodmay occur subsequently to the first time period. In addition, the secondtime period may span a different duration than the first time period.

In one example, generating the second ECG template includes generatingthe second ECG template on a predetermined schedule. In one example,generating the second ECG template includes generating the second ECGtemplate during a baselining operation initiated by a remote server. Inone example, generating the second ECG template includes generating thesecond ECG template during a baselining operation initiated by a humanoperator. In one example, generating the second ECG template includesgenerating the second ECG template during a baselining operationinitiated by the user.

In one example, generating the second ECG template includes generatingthe second ECG template during a baselining operation and the detectioncomponent is further configured to provide a notification regarding thebaselining operation prior to generating the second ECG template. Inthis example, the notification may include at least one of an audiblealarm, a spoken warning, a visual alert, a tactile alert, and a signalsent to a remote server.

In one example, the detection component is configured to generate atleast one ECG template of the first and second ECG templates bydetermining numerical coefficients of one or more matched filters basedon analysis of an identified ECG signal corresponding to the at leastone ECG template. In this example, the detection component may beconfigured to determine whether the patient is experiencing a cardiacevent based in part by filtering a signal corresponding to the ECGsignal with at least one of the one or more matched filters.

In one example, the detection component is configured to read aparameter that specifies a delay between generation of the first ECGtemplate and generation of the second ECG template and to generate thesecond ECG template after expiration of the delay. In this example, thedelay may include at least one week.

In one example, the detection component is configured to compare thefirst ECG template to the second ECG template and to discard the secondECG template responsive the second ECG template deviating from the firstECG template by a threshold measurement. In one example, generating thesecond ECG template includes generating the second ECG templateresponsive to at least one of input by the patient and expiration of apredetermined period of time since generation of the first ECG template.

In one example, the detection component is configured to associate thefirst ECG template with a first patient, to associate the second ECGtemplate with a second patient, and to identify the at least one of thefirst ECG template and the second ECG template based on a configurableparameter. In one example, the detection component is configured toassociate the first ECG template with a first patient, associate thesecond ECG template with a second patient, and to identify the at leastone of the first ECG template and the second ECG template based on anautomatic determination of an identity of a patient as either the firstor second patient from the patient's ECG signal.

In one example, the medical further includes a motion detector to detectand record historical information relating to a patient's movement,wherein the detection component is configured to identify the at leastone of the first ECG template and the second ECG template based on thehistorical information relating to the patient's movement. In thisexample, the detection component may be configured to calculate anactivity score based on the historical information relating to thepatient's movement, and where the activity score is below an activitythreshold, to identify the first ECG template as the at least one of thefirst ECG template and the second ECG template. In addition, thedetection component may be configured to identify, where the activityscore is above the activity threshold, the second ECG template as the atleast one of the first ECG template and the second ECG template.

In one example, the medical device further includes at least one antennaand the detection component is configured to transmit the at least oneof the first ECG template and the second ECG template to an externalsystem. In one example, the medical device further includes at least oneantenna and the detection component is configured to receive, from anexternal system, one or more of the first ECG template and the secondECG template.

In one example, the medical device includes at least two electrode pairsand wherein determining whether the patient is experiencing the cardiacevent includes comparing each pair of signals from the at least twoelectrode pairs with either the first ECG template or the second ECGtemplate using one or more matched filters. In this example, comparingmay include performing a signal operation based on the one or morematched filters on each pair of signals from the at least two electrodepairs and either the first ECG template or the second ECG template. Thesignal operation may include a convolution operation on a signalrepresentation of a pair of signals and either the first ECG template orthe second ECG template. In addition, the at least two electrode pairsmay include a front to back pair and a side to side pair.

In one example, the detection component is configured to determinewhether the cardiac event is a treatable arrhythmia or an untreatablearrhythmia by performing a morphology analysis of the ECG signal withrespect to the at least one of the first ECG template and the second ECGtemplate. In this example, the morphology analysis may include detectinga QRS complex in the ECG signal, and where the QRS complex is detected,determining that the cardiac event is an untreatable arrhythmia. Inanother example, detecting the QRS complex may include performing aconvolution operation on a signal representation of the ECG signal and acorresponding signal representation of at least one of the first andsecond ECG signals to determine whether one or more characteristics inthe ECG signal indicate either presence or absence of the QRS complex.In addition, the treatable arrhythmia may include either ventriculartachycardia or ventricular fibrillation and/or the untreatablearrhythmia may include supraventricular tachycardia.

In one example, the medical device includes one of a wearabledefibrillator and an automated external defibrillator. In one example,the cardiac event includes at least one of premature ventricularcontraction (PVC), ventricular fibrillation (VF), ventriculartachycardia (VT), and supraventricular tachycardia (SVT).

Still other aspects and advantages of the examples disclosed herein arediscussed in detail below. Moreover, it is to be understood that boththe foregoing information and the following detailed description aremerely illustrative examples of various aspects, and are intended toprovide an overview or framework for understanding the nature andcharacter of the claimed subject matter. Any example disclosed hereinmay be combined with any other example. References to “an example,”“some examples,” “an alternate example,” “various examples,” “oneexample,” “at least one example,” “this and other examples” or the likeare not necessarily mutually exclusive and are intended to indicate thata particular feature, structure, or characteristic described inconnection with the example may be included in at least one example. Theappearances of such terms herein are not necessarily all referring tothe same example.

Furthermore, in the event of inconsistent usages of terms between thisdocument and documents incorporated herein by reference, the term usagein the incorporated references is supplementary to that of thisdocument; for irreconcilable inconsistencies, the term usage in thisdocument controls. In addition, the accompanying drawings are includedto provide illustration and a further understanding of the variousaspects and examples, and are incorporated in and constitute a part ofthis specification. The drawings, together with the remainder of thespecification, serve to explain principles and operations of thedescribed and claimed aspects and examples.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, components that are identical or nearly identical may berepresented by a like numeral. For purposes of clarity, not everycomponent is labeled in every drawing. In the drawings:

FIG. 1 is an illustration of one example of a wearable medical device;

FIGS. 2A-2B are illustrations of one example of a medical devicecontroller for a medical device;

FIG. 3 shows an example medical device for monitoring and treatingpatients in a healthcare facility;

FIG. 4 is a functional schematic of one example of a medical devicecontroller;

FIG. 5 is a block diagram of one example of a cardiac event detector;

FIG. 6 is a block diagram of one example of an axis analyzer;

FIG. 7 is a flow diagram of one example baselining process;

FIG. 8 is a flow diagram of one example patient monitoring process;

FIG. 9 is a flow diagram of one example ECG template selection process;

FIG. 10 is a flow diagram of another example ECG template selectionprocess; and

FIG. 11 is a flow diagram of an example mode selection process.

DETAILED DESCRIPTION

Medical devices in accord with various examples disclosed herein monitora patient for cardiac events including, for example, ventriculartachycardia, ventricular fibrillation, and supraventricular tachycardia.For instance, according to some examples, a medical device includes adetection component configured to generate an ECG template for a patientand determine whether the patient is experiencing a cardiac event bycomparing an ECG signal of the patient with the ECG template. In someexamples, the medical device generates multiple ECG templates and/orupdates one or more ECG templates as appropriate for the patient. Forexample, the medical device may generate an ECG template for each stateof the patient (e.g., a resting stating and an active state) and employthe appropriate ECG template based on a current state of the patient. Inaddition, the medical device may revise templates as the sinus rhythm ofthe patient changes over time because of, for example, changing exercisehabits. For example, an ECG template as used herein can account fordeviations from typical ECG signal (PQRST points), e.g., including anoccurrence of premature ventricular contraction (PVC) and/or othernon-standard ECG information.

Medical devices disclosed herein may be invasive or non-invasive. Forexample, medical devices disclosed herein may be monitoring devices(e.g., configured to monitor a cardiac signal of a patient) with orwithout an associated treatment component. Non-invasive devices asdescribed herein are in contrast to invasive devices such as implantablemedical devices (e.g., implantable defibrillators). For example, anon-invasive medical device as disclosed herein can include an automatedexternal defibrillator (AED). Such AEDs are capable of monitoringcardiac rhythms, determining when a defibrillating shock is needed, andadministering the shock either automatically or under the control of atrained rescuer (e.g., an EMT or other medically trained personnel). TheAED may also be configured to provide cardiopulmonary resuscitation(CPR) counseling. Such an AED is available from ZOLL Medical Corporationof Chelmsford, Mass.

The non-invasive medical device as disclosed herein may be ambulatorydevices that are capable of and designed for moving with the patient asthe patient goes about their daily routine. For example, a non-invasivemedical device as disclosed herein can be ambulatory and bodily-attachedsuch as the LifeVest® wearable cardioverter defibrillator available fromZOLL Medical Corporation of Pittsburgh, Pa.

The examples of the methods and apparatuses discussed herein are notlimited in application to the details of construction and thearrangement of components set forth in the following description orillustrated in the accompanying drawings. The methods and apparatusesare capable of implementation in other examples and of being practicedor of being carried out in various ways. Examples of specificimplementations are provided herein for illustrative purposes only andare not intended to be limiting. In particular, acts, elements andfeatures discussed in connection with any one or more examples are notintended to be excluded from a similar role in any other examples.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. Any references toexamples or elements or acts of the systems and methods herein referredto in the singular may also embrace examples including a plurality ofthese elements, and any references in plural to any example or elementor act herein may also embrace examples including only a single element.References in the singular or plural form are not intended to limit thepresently disclosed systems or methods, their components, acts, orelements. The use herein of “including,” “comprising,” “having,”“containing,” “involving,” and variations thereof is meant to encompassthe items listed thereafter and equivalents thereof as well asadditional items. References to “or” may be construed as inclusive sothat any terms described using “or” may indicate any of a single, morethan one, and all of the described terms.

Example Wearable Medical Device

In one example, the medical device is a wearable medical device thatincludes a garment (e.g., a vest or belt) that is worn by the patient.The wearable medical device monitors the patient's ECG with sensingelectrodes, detects life-threatening arrhythmias, and delivers acardioverting or defibrillating shock through therapy pads if treatmentis necessary. FIG. 1 illustrates an example wearable medical device,such as a LifeVest® wearable cardioverter defibrillator available fromZOLL Medical Corporation of Chelmsford, Mass. As shown, the wearablemedical device 100 includes a harness 110 having a pair of shoulderstraps and a belt that is worn about the torso of a patient. Thewearable medical device 100 includes a plurality of ECG sensingelectrodes 112 that are attached to the harness 110 at various positionsabout the patient's body and electrically coupled to a sensor interfaceof the medical device controller 120 via a connection pod 130. Theplurality of ECG sensing electrodes 112, which may be dry-sensingcapacitance electrodes, are coupled to the medical device controller 120to monitor the cardiac function of the patient and generally include afront-back (FB) pair of ECG sensing electrodes and a side-side (SS) pairof ECG sensing electrodes. Additional ECG sensing electrodes may beprovided, and the plurality of ECG sensing electrodes 112 may bedisposed at varying locations about the patient's body.

The wearable medical device 100 also includes a plurality of therapyelectrodes 114 that are electrically coupled to the medical devicecontroller 120 via the connection pod 130 and which are configured todeliver one or more therapeutic defibrillating shocks to the body of thepatient, if it is determined that such treatment is warranted. Theconnection pod 130 electrically couples the plurality of ECG sensingelectrodes 112 and the plurality of therapy electrodes 114 to themedical device controller 120, and may include electronic circuitry. Theconnection pod 130 may also include other electronic circuitry, such asa motion sensor or accelerometer through which patient activity may bemonitored. It is appreciated that the wearable medical device 100 may bea monitoring only device and omit the therapy delivery capabilities andassociated components including, for example, the therapy electrodes114. In other examples, the wearable medical device 100 is a convertiblewearable medical device that is capable of switching between amonitoring only wearable medical device and a wearable treatment device.In these examples, the various treatment components may be packaged intovarious modules that can be attached or removed from the wearablemedical device as needed.

As shown in FIG. 1, the wearable medical device 100 may include a userinterface pod 140 that is electrically coupled to, or integrated inwith, the user interface of the medical device controller 120. The userinterface pod 140 can be attached to the patient's clothing or to theharness 110, for example, via a clip (not shown) that is attached to aportion of the interface pod 140. Alternatively, the user interface pod140 may simply be held in a person's hand. For example, such a userinterface pod 140 can be a smartwatch or a smartphone. In some examples,the user interface pod 140 may communicate wirelessly with the userinterface of the medical device controller 120, for example, using aBluetooth®, Wireless USB, ZigBee, Wireless Ethernet, GSM, or other typeof communication interface.

The user interface pod 140 includes a number of buttons by which thepatient, or a bystander can communicate with the medical devicecontroller 120, and a speaker by which the medical device controller 120may communicate with the patient or the bystander. For example, wherethe medical device controller 120 determines that the patient isexperiencing cardiac arrhythmia, the medical device controller 120 mayissue an audible alarm via a speaker on the medical device controller120 or the user interface pod 140 alerting the patient and anybystanders to the patient's medical condition. The medical devicecontroller 120 may also instruct the patient to press and hold one ormore buttons on the user interface of the medical device controller 120or on the user interface pod 140 to indicate that the patient isconscious, thereby instructing the medical device controller 120 towithhold the delivery of one or more therapeutic defibrillating shocks.If the patient does not respond, the device may determine that thepatient is unconscious, and proceed with the treatment sequence,culminating in the delivery of one or more defibrillating shocks to thebody of the patient. In implementations, prior to delivering the shock,conductive gel may be deployed to reduce an impedance seen by thetherapy electrodes during the delivery of the shock.

In another example, the functionality of the user interface pod 140 isintegrated into the housing of the medical device controller 120. FIGS.2A-2B illustrate such an example of the medical device controller 120.The controller 120 may be powered by a rechargeable battery 212. Therechargeable battery 212 may be removable from a housing 206 of themedical device controller 120 to enable a patient and/or caregiver toswap a depleted (or near depleted) battery 212 for a charged battery.The medical device controller 120 includes two response buttons 210 onopposing sides of the housing 206 of the medical device controller 120.As shown in FIGS. 2A-2B, the response buttons 210 are recessed to reducethe likelihood of accidental activation (e.g., a patient falling on theresponse button). The medical device controller 120 also includes, inthis example, a display screen 220 and a speaker 204 to enable thecommunication of audible and visual stimuli to the patient. It isappreciated that the response buttons 210 do not have to be placed onopposing sides of the housing as illustrated in FIGS. 2A-2B. Theresponse buttons 210, for example, may be located adjacent to each otherin the housing the ambulatory medical device controller. The adjacentplacement of the response buttons 210 may make it easier for individualswith smaller hands or less dexterity to engage the response buttons. Themedical device controller 120 may further include a port 202 toremovably connect sensing devices (e.g., ECG sensing electrodes 112)and/or therapeutic devices (e.g., therapy electrodes 114) to the medicaldevice controller 120.

Another example wearable medical device is the ambulatory externaldefibrillator described in FIG. 1 of U.S. Pat. No. 8,904,214, titled“SYSTEM AND METHOD FOR CONSERVING POWER IN A MEDICAL DEVICE,” issuedDec. 2, 2014 (hereinafter the “'214 patent”), which is herebyincorporated herein by reference herein in its entirety. In at least oneexample, the ambulatory defibrillator 100 illustrated in FIG. 1 of the'214 patent may employ the medical device controller 120, as disclosedin the present application, as a substitute for the portable treatmentcontroller 200 described in the ' 214 patent. In such an example, theECG electrodes and therapy pads illustrated in FIG. 1 of the '214 patentmay be logically and physically coupled to the medical device controller120. While some of the examples disclosed herein are directed towearable medical devices, the systems and methods disclosed herein maybe readily applied to other medical devices including, for example, anAutomated External Defibrillator (AED).

Example Medical Device for use in a Health Care Facility Setting

In some examples, the medical device for use in an inpatient context,e.g., for use with patients admitted to a health care facility, such as,a hospital. FIG. 3 illustrates an example hospital based medical deviceemploying the medical device controller 120. The hospital based medicaldevice may be constructed to provide cardiac monitoring and/or treatmentfor patients in a hospital setting who may be, for example, bedriddenand/or limited-mobility patients. As illustrated in FIG. 3, the hospitalbased medical device 300 includes the medical device controller 120 anda sensing component 302. The sensing component 302 includes a connector310 constructed to removably couple to the port 202 of the medicaldevice controller 120. The sensing component 302 may detect informationindicative of cardiac activity of the patient including, for example,ECG activity, tissue fluid, lung fluid, lung sounds, heart sounds,and/or patient activity. In some examples, the sensing component 302includes one or more electrodes 306. The electrodes 306 may be stick-onadhesive electrodes constructed to attach to the patient. In someexamples, the electrodes 306 may be detachable from a wire lead couplingthe electrode 306 to the connector 310. Constructing the sensingcomponent 302 to make the electrodes 306 detachable may enable thepatient and/or caregiver to periodically (e.g., every 24-48 hours ormore, as prescribed) replace the electrodes 306 without replacing theentire sensing component 302. For example, the electrodes 306 may belong term wear electrodes that are configured to be continuously worn bya patient for extended periods (e.g., 3 or more days).

In some examples, the hospital based medical device 300 may also includea treatment component 304 to provide treatment to the patient. Thetreatment component 304 may include, for example, a therapy pad 308configured to attach to the patient. The treatment component 304 may beconnected to the same connector 310 as the sensing component 302 and/oremploy a separate connector that is capable of coupling to the connector310. It is appreciated that the treatment component 304 may beintegrated into the sensing component 302 in a combinedsensing-treatment component. The combined sensing-treatment componentmay include an electrode with integrated sensing and treatment deliverycapabilities as described in the '214 patent.

Example Monitoring Medical Device

In some examples, the medical device may be a patient monitoring devicesuch as a mobile cardiac telemetry (MCT) monitor. For example, such apatient monitoring device may be configured to monitor one or more of apatient's physiological parameters. For example, a patient monitor mayinclude a cardiac monitor for monitoring a patient's cardiacinformation. Such cardiac information can include, without limitation,heart rate, ECG data, heart sounds data from an acoustic sensor, andother cardiac data. In addition to cardiac monitoring, the patientmonitor may perform monitoring of other relevant patient parameters,including glucose levels, blood oxygen levels, lung fluids, lung sounds,and blood pressure.

An example cardiac monitoring medical device (e.g., a cardiac monitor)may be similar to the wearable medical device 100 and/or the hospitalbased medical device 300 described above with reference to FIGS. 1-3 andomit, for example, the therapy electrodes 114 and/or the therapy pad308. In some implementations, the cardiac monitor is capable of anddesigned for being worn by a patient who is at risk of developingcardiac problems, but who does not yet meet criteria to be outfittedwith a medical device that includes a treatment component (e.g., adefibrillator).

In some implementations, the patient can interact with a user interfaceof the cardiac monitor to identify one or more patient symptoms. Theuser interface may include a touchscreen that provides a drop down menuor check list which, in turn, allows the patient to select a particularsymptom from a list of alternatives. Options for patient systems caninclude one or more of: feeling a skipped beat, shortness of breath,light headedness, racing heart rate, fatigue, fainting, chestdiscomfort, weakness, dizziness, and/or giddiness. In addition, thepatient can select a level of activity (e.g., light activity, moderateactivity, rigorous activity, etc.) that he or she was performing whenthe symptom occurred. In some implementations, in response to theselection by the patient, the cardiac monitor can cause a portion ofpatient physiological information (e.g., in the form of a cardiacsignal) to be captured for a length of time that is based on when thesymptom was experienced. For example, the cardiac monitor can cause aportion of an ECG signal of the patient to be captured. The portion ofthe ECG signal that is captured can be associated with the reportedsymptom and patient information.

Thus, the cardiac monitor may be prescribed so that continuous and/orevent-based data can be sent from the cardiac monitor to a remoteserver. A caregiver can access the data from the remote server anddetermine whether the patient is experiencing or has experienced acardiac problem. In some implementations, after determining that thepatient is experiencing a cardiac problem, the caregiver may instructthe patient to begin wearing a medical device with treatmentcapabilities.

Example Medical Device Controller

FIG. 4 illustrates a medical device controller 400 that is configured tomonitor the cardiac activity of a patient and/or provide therapy to thepatient as needed. The medical device controller 400 may, for example,be configured for use in a wearable medical device (e.g., medical devicecontroller 120). The medical device controller 400 has a variety ofpotential applications and is well suited to devices that notifyexternal entities of one or more events of interest (e.g., cardiacevents). Examples of devices to which the medical device controller 400is well suited include critical care medical devices, such as a wearableambulatory external defibrillator, an in-hospital defibrillator, an AED,or a mechanical chest compression device, such as the Autopulse® systemfrom ZOLL Medical Corporation of Chelmsford, Mass.

As shown in FIG. 4, the medical device controller 400 includes aprocessor 418, a sensor interface 412, a detection component 414, atherapy delivery interface 402, data storage 404 including patient data416, a communication network interface 406, a user interface 408, and abattery 410. The detection component 414 includes a mode selector 420, abaseline generator 422, and a cardiac event detector 424. The sensorinterface 412, as illustrated, is coupled to electrodes including afront-back (FB) electrode pair 426 and a side-side (SS) electrode pair428. It is appreciated that the electrode configuration and/or thenumber of electrodes may be changed to best suit the particularapplication.

In some examples, the battery 410 is a rechargeable battery thatprovides electrical power to other components within the medical device.The particular capacity and type of battery (e.g., lithium ion,nickel-cadmium, or nickel-metal hydride) employed may vary based on thedesired runtime between charges of the medical device and the powerconsumption of the components. For example, the battery 410 may beselected to provide a minimum runtime between charges of 44 hours. Inthis example, a suitable battery may include a 3 cell 4200 mAh lithiumion battery pack. It is appreciated that various mechanisms may beemployed to removably secure the battery 410 to the medical devicecontroller 400 including, for example, a latching mechanism.

According to the example illustrated in FIG. 4, the processor 418 iscoupled to the sensor interface 412, the therapy delivery interface 402,the data storage 404, the network interface 406, and the user interface408. The processor 418 performs a series of instructions that result inmanipulated data which are stored in and retrieved from the data storage404. According to a variety of examples, the processor 418 is acommercially available processor such as a processor manufactured byTexas Instruments, Intel, AMD, Sun, IBM, Motorola, Freescale, and ARMHoldings. However, the processor 418 may be any type of processor,multiprocessor or controller, whether commercially available orspecially manufactured. For instance, according to one example, theprocessor 418 may include a power conserving processor arrangement suchas described in the '214 patent. In another example, the processor 418is an Intel® PXA270.

In addition, in some examples, the processor 418 may be configured toexecute a conventional operating system. The operating system mayprovide platform services to application software, such as some examplesof the detection component 414 which is discussed further below. Theseplatform services may include inter-process and network communication,file system management and standard database manipulation. One or moreof many operating systems may be used, and examples are not limited toany particular operating system or operating system characteristic. Forinstance, operating systems can include a Windows based operatingsystem, OSX, or other operating systems. For instance, in some examples,the processor 418 may be configured to execute a real-time operatingsystem (RTOS), such as RTLinux, or a non-real time operating system,such as BSD or GNU/Linux.

In some examples, the detection component 414 is configured to monitorthe cardiac activity of the patient and identify cardiac eventsexperienced by the patient. The detection component 414 is described ingreater detail below with reference to FIGS. 5-10. The detectioncomponent 414 may be implemented using hardware or a combination ofhardware and software. For instance, in one example, the detectioncomponent 414 is implemented as a software component that is storedwithin the data storage 412 and executed by the processor 418. In thisexample, the instructions included in the detection component 414program the processor 418 to monitor the cardiac activity of the patientand identify cardiac events experienced by the patient. In otherexamples, the detection component 414 may be an application-specificintegrated circuit (ASIC) that is coupled to the processor 418. Thus,examples of detection component 414 are not limited to a particularhardware or software implementation.

In some examples, the components disclosed herein, such as the detectioncomponent 414, may read parameters that affect the functions performedby the components. These parameters may be physically stored in any formof suitable memory including volatile memory, such as RAM, ornonvolatile memory, such as a flash memory or magnetic hard drive. Inaddition, the parameters may be logically stored in a propriety datastructure, such as a database or file defined by a user modeapplication, or in a commonly shared data structure, such as anapplication registry that is defined by an operating system. Inaddition, some examples provide for both system and user interfaces, asmay be implemented using the user interface 408, that allow externalentities to modify the parameters and thereby configure the behavior ofthe components.

The data storage 404 includes a computer readable and writeablenonvolatile data storage medium configured to store non-transitoryinstructions and data. In addition, the data storage 404 includesprocessor memory that stores data during operation of the processor 418.In some examples, the processor memory includes a relatively highperformance, volatile, random access memory such as dynamic randomaccess memory (DRAM), static memory (SRAM) or synchronous DRAM. However,the processor memory may include any device for storing data, such as anon-volatile memory, with sufficient throughput and storage capacity tosupport the functions described herein. According to several examples,the processor 418 causes data to be read from the nonvolatile datastorage medium into the processor memory prior to processing the data.In these examples, the processor 418 copies the data from the processormemory to the non-volatile storage medium after processing is complete.A variety of components may manage data movement between thenon-volatile storage medium and the processor memory and examples arenot limited to particular data management components. Further, examplesare not limited to a particular memory, memory system or data storagesystem.

The instructions stored on the data storage 404 may include executableprograms or other code that can be executed by the processor 418. Theinstructions may be persistently stored as encoded signals, and theinstructions may cause the processor 418 to perform the functionsdescribed herein. The data storage 404 also may include information thatis recorded, on or in, the medium, and this information may be processedby the processor 418 during execution of instructions. The medium may,for example, be optical disk, magnetic disk or flash memory, amongothers, and may be permanently affixed to, or removable from, themedical device controller 400.

In some examples, the patient data 416 includes ECG templates associatedwith one or more patients. The ECG templates may be stored as, forexample, a series of matched filter coefficients. The stored matchedfilter coefficients may be employed during monitoring by, for example, amatched filter to compare the received ECG signal from the patient withthe ECG template associated with the patient. As illustrated in FIG. 4,the detection component 414 and the patient data 416 are separatecomponents. However, in other examples, the detection component 414 andthe patient data 416 may be combined into a single component orre-organized so that a portion of the data included in the detectioncomponent 414, such as executable code that causes the processor 418 togenerate ECG templates and monitor any cardiac events experienced by thepatient, resides in the patient data 416, or vice versa. Such variationsin these and the other components illustrated in FIG. 4 are intended tobe within the scope of the examples disclosed herein.

The patient data 416 may be stored in any logical construction capableof storing information on a computer readable medium including, amongother structures, flat files, indexed files, hierarchical databases,relational databases, or object oriented databases. These datastructures may be specifically configured to conserve storage space orincrease data exchange performance. In addition, various examplesorganize the patient data 416 into particularized and, in some cases,unique structures to perform the functions disclosed herein. In theseexamples, the data structures are sized and arranged to store values forparticular types of data, such as integers, floating point numbers,character strings, arrays, linked lists, and the like.

As shown in FIG. 4, the medical device controller 400 includes severalsystem interface components 402, 406, and 412. Each of these systeminterface components is configured to exchange, i.e. send or receive,data with one or more specialized devices that may be located within thehousing of the medical device controller 400 or elsewhere. Thecomponents used by the interfaces 402, 406, and 412 may include hardwarecomponents, software components or a combination of both. Within eachinterface, these components physically and logically couple the medicaldevice controller 400 to the specialized devices. This physical andlogical coupling enables the medical device controller 400 tocommunicate with and, in some instances, power or control the operationof the specialized devices. These specialized devices may includephysiological sensors, therapy delivery devices, and computer networkingdevices.

According to various examples, the hardware and software components ofthe interfaces 402, 406, and 412 implement a variety of coupling andcommunication techniques. In some examples, the interfaces 402, 406, and412 use leads, cables or other wired connectors as conduits to exchangedata between the medical device controller 400 and specialized devices.In other examples, the interfaces 402, 406, and 412 communicate withspecialized devices using wireless technologies such as radio frequencyor infrared technology. The software components included in theinterfaces 402, 406, and 412 enable the processor 418 to communicatewith specialized devices. These software components may include elementssuch as objects, executable code, and populated data structures.Together, these software components provide software interfaces throughwhich the processor 418 can exchange information with specializeddevices. Moreover, in at least some examples where one or morespecialized devices communicate using analog signals, the interfaces402, 406, and 412 further include components configured to convertanalog information into digital information, and vice versa, to enablethe processor 418 to communicate with specialized devices.

As discussed above, the system interface components 402, 406, and 412shown in the example of FIG. 4 support different types of specializeddevices. For instance, the components of the sensor interface 412 couplethe processor 418 to one or more physiological sensors such as a bodytemperature sensors, respiration monitors, and electrocardiogram (ECG)sensing electrodes, one or more environmental sensors such asatmospheric thermometers, airflow sensors, video sensors, audio sensors,accelerometers, GPS locators, and hygrometers, or one or more motiondetection sensors such as altimeters, accelerometers, and gyroscopes. Inthese examples, the sensors may include sensors with varying samplingrates, including wireless sensors. The sensor interface 412, asillustrated, is coupled to four ECG sensing electrodes that form afront-back (FB) electrode pair 426 and a side-side (SS) electrode pair428. The sensor interface may include various circuitry to amplify theECG signal detected by the electrodes, condition the received ECGsignal, and/or digitize the ECG signals as described in U.S. Pat. No.8,600,486, titled “METHOD OF DETECTING CLIPPING IN A WEARABLE AMBULATORYMEDICAL DEVICE” and issued on Dec. 3, 2013 (hereinafter the “'486patent”), which is hereby incorporated herein by reference in itsentirety. It is appreciated that the particular number of ECG sensingelectrodes coupled to the sensor interface 412 and/or the pairing of theECG sensing electrodes may vary based on the specific implementation.

In some examples, the components of the therapy delivery interface 402couple one or more therapy delivery devices, such as capacitors,defibrillator electrodes, pacing electrodes or mechanical chestcompression devices, to the processor 418. It is appreciated that thefunctionality of the therapy delivery interface 402 may be incorporatedinto the sensor interface 412 to form a single interface coupled to theprocessor 418. In addition, the components of the network interface 406couple the processor 418 to a computer network via a networking device,such as a bridge, router or hub. According to a variety of examples, thenetwork interface 406 supports a variety of standards and protocols,examples of which include USB (via, for example, a dongle to acomputer), TCP/IP, Ethernet, Wireless Ethernet, Bluetooth, ZigBee,M-Bus, CAN-bus, IP, IPV6, UDP, DTN, HTTP, HTTPS, FTP, SNMP, CDMA, NMEAand GSM. It is appreciated that the network interface 406 of medicaldevice controller 400 may enable communication between other medicaldevice controllers within a certain range.

To ensure data transfer is secure, in some examples, the medical devicecontroller 400 can transmit data via the network interface 406 using avariety of security measures including, for example, TLS, SSL or VPN. Inother examples, the network interface 406 includes both a physicalinterface configured for wireless communication and a physical interfaceconfigured for wired communication. According to various examples, thenetwork interface 406 enables communication between the medical devicecontroller 400 and a variety of personal electronic devices including,for example, computer enabled glasses, wristwatches, earpieces, andphones.

In one example, the network interface 406 is also capable oftransmitting and/or receiving information to assist in monitoring thecardiac function of the patient. This may be accomplished through one ormore antennas integrated with or coupled to the network interface 406,and consequently coupled to the processor 418. For example, the one ormore antennas may receive information representative of the ECG templateassociated with the patient. The wireless signals received by theantennas may be analyzed by the processor 418 to generate an ECGtemplate for the patient. The network interface 406 may also transmitone or more generated ECG templates to an external system. For example,the medical device may transmit the ECG template associated with apatient to a health care provider of the patient. The health careprovider may provide the ECG template to one or more other medicaldevices employed to provide treatment to the patient.

Thus, the various system interfaces incorporated in the medical devicecontroller 400 allow the device to interoperate with a wide variety ofdevices in various contexts. For instance, some examples of the medicaldevice controller 400 are configured to perform a process of sendingcritical events and data to a centralized server via the networkinterface 406. An illustration of a process in accord with theseexamples is disclosed in U.S. Pat. No. 6,681,003, titled “DATACOLLECTION AND SYSTEM MANAGEMENT FOR PATIENT-WORN MEDICAL DEVICES,” andissued on Jan. 20, 2004, which is hereby incorporated herein byreference in its entirety.

As illustrated in FIG. 4, the therapy delivery interface 402 is optionaland may not be included in every example. For instance, an MCT monitoror other monitoring device may employ the medical device controller 400to issue alarms but may not include a therapy delivery interface 402 totreat cardiac abnormalities. Similarly, an ambulatory defibrillator mayinclude the medical device controller 400 to provide alarm functionalitybut may not include a network interface 406 where, for example, theambulatory defibrillator is designed to rely on the user interface 408to announce alarms.

The user interface 408 shown in FIG. 4 includes a combination ofhardware and software components that allow the medical devicecontroller 400 to communicate with an external entity, such as a patientor other user. These components may be configured to receive informationfrom actions such as physical movement, verbal intonation, or thoughtprocesses. In addition, the components of the user interface 408 canprovide information to external entities. Examples of the componentsthat may be employed within the user interface 408 include keyboards,mouse devices, buttons, microphones, electrodes, touch screens, printingdevices, display screens, and speakers. In some examples, the electrodesinclude an illuminating element, such as an LED. In other examples, theprinting devices include printers capable of rendering visual or tactile(Braille) output.

In some examples, the user interface 408 may be configured to provideinformation to external entities regarding a cardiac event experiencedby the patient. For example, the user interface 408 may provide an alarmindicting that the patient is experiencing an arrhythmia. In theseexamples, the user interface may also receive input from the patientregarding the cardiac event. For example, the user interface 408 mayissue an alarm requesting the patient to interact with at least oneelement of the user interface 408 (e.g., push a button) to delay theadministration of therapy (e.g., a defibrillating shock) and/oracknowledge the alarm.

In some examples, the detection component 414 monitors the cardiaccondition of the patient. The detection component 414 may monitor thecardiac condition of the patient by generating an ECG template for thepatient and comparing the ECG template with the ECG signal of thepatient to identify cardiac events. For example, comparing the ECGtemplate with the ECG signal of the patient can include filtering theincoming ECG signal through a filter comprising the ECG template asdescribed in further detail below. In an implementation, the filteringoperation can include a predetermined mathematical operation (e.g., aconvolution) involving a signal representation of the ECG template andthe ECG signal of the patient. The functions of the detection component414 may be divided between a baselining mode (e.g., a “learn mode”)where ECG templates are generated, and a monitoring mode where the ECGtemplates are compared with the ECG signal of the patient. Asillustrated in FIG. 4, the baseline generator 422 performs the variousprocesses associated with baselining mode while the cardiac eventdetector 424 performs the various processes associated with themonitoring mode. The mode selector 420 of the detection component 414controls the operating mode of the medical device (e.g., whether themedical device is in a monitoring mode or a baselining mode). It isappreciated that the particular architecture shown in FIG. 4 is forillustration only and other architectures and/or modes may be employedby the detection component 414.

Example Baselining

The baseline generator 422 generates an ECG template associated with thepatient. The ECG template may be indicative of a normal sinus rhythm ofthe patient. In some examples, the ECG template may also account forrate and morphological variations in patient populations in composingthe template. For example, the ECG template can account for ectopicbeats such as premature ventricular contractions (PVCs). The ECGtemplate is employed by the cardiac event detector 424 to determinewhether the patient is experiencing a cardiac event. FIG. 7 illustratesan example baselining process 700 performed by, for example, thebaseline generator 422. In some examples, the baseline mode of thedevice can be accessed for performing the baselining This process can beperformed before active patient monitoring operation begins. Asdiscussed below, in some implementations, the process can be repeatedperiodically, e.g., once every two weeks, or when prompted by anexternal event (e.g., user-triggered event) or an internal event (e.g.,automated detection of a triggering condition).

Example triggering conditions can include, without limitation, one ormore of a change in patient profile information or data (e.g., through amanual or automated remote or local download process), device or userinitiated periodic or aperiodic self-tests, mechanical impact detection(e.g., when the device is subject to forces beyond a predeterminedthreshold), tampering of the device, assembly and/or disassembly eventsinvolving the device, excess temperature and/or moisture events, batterychange events, post-shock delivery (e.g., a period of time after a shockhas been delivered), an arrhythmia warning or alert event (e.g., whenthe patient is conscious and able to respond by pushing the responsebuttons), actuation of the response buttons (e.g., actuation of thebuttons in a predetermined manner), changes in and/or tampering of geldeployment mechanism, detected excessive cabling and/or device strains,error conditions thrown by monitor software, and monitor softwareupdates.

During the ECG baseline sequence, the patient's normal rhythm can berecorded and analyzed as described below. A user interface can providemessages and interface with a user (either the patient or a caregiver)to allow the recording of the ECG data. When the user interface receivesnotification that the baseline process has successfully completed, theuser can be notified by a display and/or an alarm.

In an example, the baselining process can include the acts of recordingthe patient ECG signal 702, determining a composite QRST waveform basedon the recorded patient ECG signal 704, and identifying filterparameters based on the QRST waveform 706 as the ECG template. Thebaselining process 700 may also include transmitting the filterparameters to an external system 708 (e.g., a computer system of ahealth care provider associated with the patient) for storage, review,and/or analysis. For example, a caregiver may remotely accept or rejecta recorded ECG template without requiring that the patient be physicallypresent in the caregiver's office.

In act 702, the medical device records the ECG signal of the patient. Asdiscussed above, the medical device may include various sensingelectrodes placed around the body of the patient. In some examples, themedical device includes multiple pairs of ECG electrodes (e.g., afront-back electrode pair and a side-side electrode pair). In theseexamples, the medical device may record the ECG signal received fromboth pairs simultaneously. The recorded ECG signal of the patient fromwhich the ECG template is derived may be stored locally in, for example,the patient data 416 of the medical device controller 400. It isappreciated that the duration of the ECG signal recording may vary basedon the particular application. In some examples, the duration of the ECGsignal recorded is between one minute and five minutes. In someexamples, the duration of the ECG signal recorded for deriving an ECGtemplate is at least 10 seconds. In an implementation, the baselinegenerator 422 can include a morphology analyzer for detecting QRScomplexes in the recorded ECG signal during the derivation of the ECGtemplate. For example, the ECG template can be obtained as a complexcomposite by, e.g., combining averaged ECG signals from side-to-sideelectrodes and front-to-back electrodes. For example, such a compositetemplate can have a duration in a range from 0.5 to 2 seconds. In someimplementations, however, the composite template can be configured tohave durations of less than 0.5 seconds or more than 2 seconds. The ECGtemplate can be obtained such that the QRS complex resides in a middleof the ECG template.

In act 704, the medical device determines, e.g., an average of the QRSTwaveforms within the recorded ECG signal. A person of ordinary skill inthe art, given the benefit of this disclosure, can appreciate thatrather than an average, any other method for determining a compositerepresenting the recorded ECG signal may be used. For example, therecorded ECG signal of the patient may include two minutes of ECG dataof a patient with a normal heart rate between 60 and 100 beats perminute (bpm). In this example, the recorded ECG data may include between120-200 individual QRST waveforms associated with the 120-200 heartbeatsof the patient over the two minute period. Each of the QRST waveformsmay be identified and composed together (e.g., averaged) to form a QRSTwaveform template representative of a normal sinus rhythm of thepatient.

Once the QRST waveform template is generated by the baseline generator422, the QRST waveform template may be compared with the QRST waveformsreceived from the patient to facilitate the identification of cardiacevents. An example method of comparing a known signal shape (e.g., theQRST waveform template) with another signal (e.g., the incoming ECGsignal of the patient) is by constructing a matched filter and filteringthe signal with the matched filter. Matched filters may include, forexample, filters with an impulse response similar to a conjugatetime-reversed version of the template signal. Filtering a signal by amatched filter may be equivalent to convolving the signal with aconjugate time-reversed version of the template signal in thetime-domain and/or multiplying a frequency domain representation of thesignal with the frequency domain representation of the template signal.The output of a matched filter is a correlation between the signalreceived by the matched filter and the template associated with thematched filter. Employing a matched filter may be an advantageouscomparison method because the correlation values provided by matchedfilters are generally very robust to additive noise in the receivedsignal including, for example, Additive White Gaussian Noise (AWGN).Matched filters may be implemented, for example, as a finite impulseresponse (FIR) filter. These FIR filters may be represented by a seriesof filter coefficients (e.g., between 100-200 numerical coefficients)that create a filter with the desired impulse response. Accordingly, inact 706, the medical device generates the appropriate filtercoefficients based on the QRST waveform template to form the matchedfilter.

In some examples, the baseline generator 422 may transmit the filtercoefficients associated with the matched filter to an external system asillustrated by act 708. For example, the filter coefficients may beprovided to a computer system of a health care provider associated withthe patient. The computer system of the health care provider maywirelessly transmit the filter coefficients to medical devices employedto provide treatment to the patient.

It is appreciated that other methods may be employed to generate thetemplate, and the techniques described herein are not to be limited tothe specific examples described here. For example, the baselinegenerator may receive the filter coefficients descriptive of the matchedfilter from an external system. In addition, multiple ECG templates maybe generated and/or other patient related information may be recordedwhile the patient ECG information is recorded. For example, the baselinegenerator 422 may record the activity level of the patient in act 702while the ECG signal of the patient is recorded. The activity level maybe monitored by recording the movement of the patient detected by anaccelerometer (e.g., coupled to the sensor interface 412). In thisexample, an activity score may be derived from the detected activitylevel during ECG recording and be associated with the generated ECGtemplate. The activity score associated with the ECG template may beused in the cardiac monitoring processes performed by the cardiac eventdetector 424 to select an appropriate ECG template to monitor thepatient as described below with reference to FIGS. 8 and 9.

In some examples, the ECG template may be associated with additionalpatient parameters recorded and stored along with the ECG template. Insome situations, such additional information can provide detailsregarding the circumstances in which the ECG template was recorded. Forexample, if the ECG template recording was prompted by an uptick inpatient activity, an average heart rate during the baselining periodand/or during a period of time preceding the baselining or the prompt toperform the baselining, e.g., one week before, may be recorded andstored with the ECG template.

Example Cardiac Event Detection Circuitry

The cardiac detector 424 monitors the ECG signal of the patient todetect cardiac events experienced by the patient. The cardiac detector424 may also determine which particular cardiac event the patient iscurrently experiencing including, for example, ventricular fibrillation,ventricular tachycardia, and supraventricular tachycardia. In someexamples, the cardiac detector 424 employs one or more ECG templatesgenerated by the baseline generator 422 to compare with the ECG signalof the patient. As briefly described above, the comparison between theECG signal of the patient and the ECG template may be performed byemploying one or more matched filters. The cardiac detector 424 mayanalyze the phase and/or magnitude of the matched filter output (e.g.,the correlation signal) to identify cardiac events. For example, thecardiac detector 424 may determine that the patient is not experiencinga cardiac event originating in a heart ventricle responsive to the peakmagnitude of the correlation signal occurring at, or near, a zero phasecrossing of the correlation signal. As the peak in the correlationmagnitude moves away from the zero phase crossing point (e.g., greaterthan 10-20°), the cardiac detector 424 may determine that a cardiacevent originating in a heart ventricle is present including, forexample, ventricular tachycardia or ventricular defibrillation. Thecardiac detector 424 may further analyze the heart rate of the patientto identify cardiac events originating in other areas of the heart(e.g., in an atrium).

FIG. 5 illustrates a block diagram of an example cardiac event detector500 for detecting cardiac events experienced by the patient by variousmorphology analysis techniques (e.g., cardiac event detector 424). Thecardiac event detector 500 receives electrode information 502 from thevarious electrodes in the medical device. The electrode information 502may include information from, for example, a front-back electrode pair(e.g., front-back electrode pair 426) and a side-side electrode pair(e.g., side-side electrode pair 428). The cardiac event detector 500provides an arrhythmia status 522 indicating whether the patient isexperiencing an arrhythmia. The arrhythmia status 522 may also includean indication of the particular type of arrhythmia the patient isexperiencing including, for example, an indication of whether thepatient is experiencing supraventricular tachycardia, ventriculartachycardia, or ventricular fibrillation. It is appreciated that thevarious blocks included within the cardiac event detector 500 may beimplemented in hardware, software, or a combination of hardware andsoftware. For example, the electrode information 502 may include adigitized ECG signal of the patient and each of the blocks may befunction blocks executed by a Digital-Signal-Processor (DSP).

The high frequency (HF) noise analyzer block 510, automatic gain controlblock 512, and electrode falloff sensing block 514 each generateinformation indicative of the quality of the ECG information beingreceived. For example, the HF noise analyzer block 510 identifies highfrequency noise in the ECG information and provides an HF noiseindicator illustrative of the level of high frequency noise detected.The automatic gain control block 512 may control the gain of one or moregain stages in an amplifier cascade to increase the magnitude of the ECGsignal as described in the '486 patent. The automatic gain control block512 may also determine whether the ECG signal is experiencing distortion(e.g., soft clipping or hard clipping) and provide an indication ofsignal distortion. The electrode falloff sensing block 514 determineswhether the electrodes have fallen off the patient and provides anelectrode contact indicator. The electrode quality information providedby the HF noise analyzer block 510, the automatic gain control block512, and the electrode falloff sensing block 514 may be received by thesignal quality monitor 518. The signal quality monitor 518 analyzes thevarious parameters received by the HF noise analyzer 510, the automaticgain control 512, and the electrode falloff sensing block 514 to providea final signal quality indicator to the decision logic block 520. It isappreciated that the signal quality monitor block 518 may also receiveelectrode quality information from the spectrum analyzer block 508 inthe form of a low frequency (LF) noise indicator.

The QRS detector block 504, axis analyzer 506, and spectrum analyzer 508each analyze the incoming electrode information 502 and generate heartrate information. The QRS detector block 504 determines the heart rateof the patient based on the electrode information 502. The QRS detectorblock 504 may also determine the heart rate stability of the patientbased on heart rate changes. The QRS detector block 504 provides thedetermined heart rate and heart rate stability to the rate analyzerblock 516. The axis analyzer block 506 may also determine the electricalaxis of the heart of the patient using various morphology techniques.The axis analyzer block 506 provides an axis rate to the rate analyzerblock 516. In addition, the axis analyzer block 506 determines thevector of the electrical axis of the heart and can output an axisvalidity signal indicating whether the patient is experiencing atreatable condition or a non-treatable condition. The various processesperformed by the axis analyzer 506 are described in more detail belowwith reference to FIG. 6. The axis information is passed to the decisionlogic block 520 to determine whether the patient is experiencing anarrhythmia and/or identify the particular type of arrhythmia the patientis experiencing. The spectrum analyzer 508 measures and evaluates thefrequency components of the electrode information 502. The spectrumanalyzer 508 may transform the electrode information into the frequencydomain by, for example, a Fast Fourier Transform (FFT). The spectrumanalyzer 508 determines a spectral heart rate that is provided to therate analyzer block 516.

The rate analyzer block 516 receives heart rate information from the QRSdetector block 504, the axis analyzer block 506, and the spectrumanalyzer block 508. The rate analyzer block 516 determines whether thepatient is experiencing an elevated heart rate based on the heart rateinformation and provides an indication of the high heart rate to thedecision logic block 520. The rate analyzer block 516 may determine theheart rate of the patient by determining whether the heart rates fromthe QRS detector 504 are equal across the electrode pairs (e.g.,side-side electrode pair and front-back electrode pair). If the ratesare equal, the rate analyzer block 516 may assume that heart rate fromthe QRS detector block 504 is the proper rate. However, if the ratestability signal begins to change or if the rates across the electrodepairs begin to differ, the rate analyzer block 516 can use the axis ratefrom the axis analyzer 506 or spectral rate from the spectrum analyzerto determine the proper heart rate. The rate analyzer block 516 cantrack the stability of the axis rate and the spectral rate to determinethe reliability of the respective rates. In addition, the rate analyzer516 can reevaluate the rate inputs individually and independently or incomparison to one another.

The decision logic 520 receives the indication of a high heart rate fromthe rate analyzer 516, an indication of axis validity from the axisanalyzer 506, and a signal quality indicator from the signal qualitymonitor 518. The decision logic 520 employs the heart rate, heart axis,and signal quality information to determine whether the patient isexperiencing an arrhythmia and/or identify the arrhythmia beingexperienced by the patient. For example, the decision logic block 520may employ the signal quality indicator to determine the reliability ofthe heart axis information and heart rate information received from theaxis analyzer 506 and rate analyzer 516, respectively. For example, thedecision logic 520 may ignore information from the axis analyzer 506 andthe rate analyzer 516 while the ECG signal quality is very poor.

In cases where the electrode information is of sufficient quality, thedecision logic block 520 may determine whether the patient isexperiencing an arrhythmia based on the heart axis information and heartrate information. For example, the decision logic 520 may employ theheart rate information to determine whether the patient is experiencingan arrhythmia and employ the heart axis information to discriminatebetween one or more types of arrhythmias. As described in more detailbelow with reference to the axis analyzer 506, a patient having peaks incorrelation between the ECG template and the ECG signal of the patientat a different time than phase zero crossings in the correlation signalis likely experiencing an arrhythmia originating from a heart ventricle.Accordingly, the decision logic block 520 may analyze the axisinformation to discriminate between arrhythmias originating in a heartventricle (e.g., ventricular tachycardia and ventricular fibrillation)and arrhythmias originating from other areas of the heart (e.g.,supraventricular tachycardia).

Referring to FIG. 6, a block diagram of an example axis analyzer 600(e.g., axis analyzer 506) is illustrated. The axis analyzer 600 receivesECG input signals from one or more electrode pairs and employsmorphology analysis techniques to analyze the electrical axis of theheart of the patient. The axis analyzer provides heart axis information634 and axis rate information 636 to other components of, for example,the cardiac event detector 500. As discussed above with reference to thecardiac event detector 500, the blocks illustrated in the axis analyzer600 may be implemented in hardware, software, or a combination ofhardware and software.

As illustrated in FIG. 6, the axis analyzer 600 receives ECG signalsfrom a side-side electrode pair 602A and a front-back electrode pair602B. The ECG signals received from the side-side electrode pair 602Aand the front-back electrode pair 602B are filtered by bandpass filters604A and 604B, respectively, to remove any noise contained outside thefrequency band of interest. The filtered ECG signals are passed tomatched filters 606A and 606B to determine a correlation between the ECGsignals of the patient and an ECG template of the patient. In addition,the filtered ECG signals are converted into a complex signal by thecomplex signal generator 620 and provided to the complex matched filter622. As described above, the matched filters may be constructed based onvarious coefficients determined by the baseline generator 422 while thedevice is operating in a baselining mode.

Referring to the complex matched filter 622, the output includes a phasesignal provided to delay block 624 and a magnitude signal provided todelay block 628. The delay blocks 624 and 628 delay the signal by apredetermined amount of time (e.g., seven sample periods). The delayblocks 624 and 628 allow the output of the level comparator blocks 616A,616B, and 632 and phase detector block 626 to be in time sync.Accordingly, the particular delay employed may vary based on theparticular architecture of the axis analyzer 600. The phase detector 626continuously monitors the phase signal received from the delay block 624and identifies zero crossings in the phase signal. The phase detector626 provides a signal to the correlation test block 618 responsive todetecting a zero crossing in the phase signal. The threshold controlblock 630 receives the magnitude signal delay block 628 and determines athreshold to be employed by the level comparator 632 based on thehistory of the magnitude signal. The level comparator 632 compares themagnitude signal from the delay block 628 with the threshold set bythreshold control block 630. The level comparator 632 provide a signalto the correlation test block 618 that indicates a peak detection in themagnitude signal responsive to the magnitude signal being above thethreshold. Returning to the threshold control block 630, the thresholdmay be permitted to vary within a preset range of values. In some cases,the threshold may be set to less than 90% of previously detected peaklevels. Adjustment of the threshold allows the axis analyzer 600 totrack variations in the correlation caused by, for example, changes inreceived signal quality. Adjusting the threshold also may be employed tocontrol the sensitivity of the axis detector.

Returning to matched filters 606A and 606B, the output correlations ofthe matched filters 606A and 606B are provided to median filters 610Aand 610B, respectively. The median filters 610A and 610B determine themedian of the magnitude values provided by the matched filters 606A and606B. The median values determined by the median filters 610A and 610Bare subtracted from the correlations from the matched filters, afterbeing delayed by delay blocks 608A and 608B to keep in time sync, insummation blocks 612A and 612B, respectively. Removing the median valuesfrom the correlation may help to distinguish correlation peaks. Thesummation blocks 612A and 612B may also apply a floor operator of zeroto convert any negative values to zero. It is appreciated that thesummation blocks 612A and 612B may be implemented in a DSP by, forexample, subtracting two values and applying a floor operator or bycircuit components by, for example, a summation circuit followed by arectification circuit.

The output from the summation blocks 612A and 612B is provided tothreshold control blocks 614A and 614B that each generate a thresholdfor level comparator blocks 616A and 616B, respectively. As describedabove with reference to threshold control block 630 and level comparator632, the threshold control blocks 614A and 614B adjust the threshold fordetermining a peak in magnitude based on previous correlation peakvalues. The level comparator blocks 616A and 616B provide signals to thecorrelation test block 618 indicative of whether a peak in correlationwas detected.

The correlation analysis block 618 examines the timing relationship ofthe output of phase detector 626 (e.g., the timing of phase zerocrossings) and level comparators 616A, 616B, and 632 (e.g., the timingof magnitude peaks) and provides heart axis information 634 to otherblocks within, for example, cardiac event detector 500. Patients with anormal sinus rhythm generally have a peak in correlation magnitude atapproximately the same time as a phase zero crossing. As the timing ofthe peaks in magnitude separates from the timing of zero crossings, thelikelihood of the patient experiencing a cardiac event increases. Thecorrelation analysis block 618 examines the timing and determineswhether a treatable condition exists based on the timing information.For example, the correlation analysis block 618 may identify erraticchanges in timing associated with cardiac events. The occurrence of asingle magnitude peak at a given instant of time, that does not have acorresponding zero phase crossing point, may not be significant.However, a phase shift away from the magnitude peaks that is maintainedover a period of time or an erratically shifting phase variation may besignificant. Example patient sinus rhythms and the associatedcorrelations are illustrated in U.S. Pat. No. 5,944,669, titled“APPARATUS AND METHOD FOR SENSING CARDIAC FUNCTION” and issued on Aug.31, 1999, which is hereby incorporated herein by reference in itsentirety. The correlation analysis block 618 may analyze thecharacteristics of the timing shift to determine whether the arrhythmiais a treatable arrhythmia (e.g., ventricular tachycardia or ventricularfibrillation) or a non-treatable arrhythmia (e.g., supraventriculartachycardia). For example, the ventricular response is not greatlyaffected in a supraventricular tachycardia originating in the atrium(although the heart rate may increase). Therefore, a radical shiftbetween the phase zero crossings and the magnitude peaks does not occur.The ventricular response, however, in ventricular tachycardia orventricular fibrillation is directly impacted and a radical shiftbetween the phase zero crossings and the magnitude peaks generallyoccurs.

Example Cardiac Detection

Having described various system architectures that may be suitable forthe cardiac event detector 424 to detect cardiac events based on an ECGtemplate, various example processes implemented by the cardiac detector424 will now be described. In some of these example processes, a cardiacevent detector, such as the cardiac event detector 424, selects anappropriate ECG template to utilize in morphology analysis. For example,the device may include multiple ECG templates corresponding to differentpersons in a household. In some implementations, prior to use, thepatient, family member, or other caregiver may be prompted to select theappropriate person for whom the device is to be configured such that theappropriate ECG template is selected. In some examples, the cardiacevent detector 424 can detect a patient ECG signal and based on thedetected ECG signal automatically determine the appropriate ECG template(e.g., the ECG template corresponding to the person being monitored) touse for the monitoring. For example, the cardiac event detector 424 maybase a determination of the appropriate ECG template on the detection ofone or more features in the ECG signal. For example, a first member of ahousehold may have certain recurring ECG features or morphology thatare/is different from ECG features or morphology in a second member of ahousehold. Such features can include, without limitation, a width andheight of the QRS complex, the prominence of the T wave, and a lengthand/or ST segment.

In addition, at least one of these example processes includes possibleactions the cardiac event detector 424 may initiate upon detection of acardiac event. Referring to FIG. 8, an example patient monitoringprocess 800 is illustrated as performed by, for example, a cardiac eventdetector, such as the cardiac event detector 424. The patient monitoringprocess 800 includes the acts of receiving patient ECG information 802,selecting an ECG template 804, and comparing the patient ECG informationwith the selected ECG template 806. In some examples, the medical deviceis a medical device capable of providing therapy to the patient and thepatient monitoring process 800 includes the act of providing therapy tothe patient 808.

In act 802, the cardiac event detector receives ECG information from,for example, one or more ECG electrodes attached to the patient. The ECGinformation may include, for example, a digitized ECG signal.

In act 804, the cardiac event detector selects an ECG template tocompare with the ECG information of the patient. In some examples, thecardiac event detector may select a template associated with theparticular patient connected to the medical device. The cardiac detectormay uniquely identify the patient based on a configurable parameter orone or more characteristics of the received ECG information. It isappreciated that the cardiac event detector may select a particular ECGtemplate based on parameters other than patient identity. For example,the cardiac detector may filter the patient ECG signal through thevarious matched filters associated with the ECG templates stored inmemory and select the ECG template associated with the matched filtersthat yielded the highest correlation values. For example, the detectormay build a composite ECG signal based on averaging detected ECG datapoints over a period a time (e.g., 20 seconds). The detector can thencompare each averaged point with a corresponding point in the ECGtemplate and calculate a corresponding error value. The detector canselect an ECG template associated with the lowest error value (e.g.,based on a lowest mean error rate). It should be understood that anytechnique for calculating an average deviation from the ECG templatecoefficients may be used.

In some cases, the patient may have been recently administered a shock,and as a result his or her ECG signal may differ characteristically fromthe ECG signal prior to the shock event. As a result, the patient mayneed to be re-baselined in accordance with the principles describedherein. Accordingly, the template selection process 900 may use thenewly obtained ECG template for comparison purposes. Additional exampletemplate selection processes are described below with reference to FIGS.9 and 10.

In act 806, the cardiac event detector compares the received ECGinformation with the selected ECG template to determine whether thepatient is experiencing a cardiac condition. The cardiac event detectormay perform the comparison by employing one or more matched filters asdescribed above with reference to FIGS. 5 and 6. The cardiac eventdetector may identify a particular type of arrhythmia based on thecomparison and/or determine whether the arrhythmia is a treatablearrhythmia. For example, an arrhythmia originating from a heartventricle (e.g., ventricular tachycardia and ventricular fibrillation)may be a treatable arrhythmia while an arrhythmia originating from abovethe ventricular (e.g., supraventricular tachycardia) may be anuntreatable arrhythmia.

In some examples, the cardiac event detector (in act 806) may comparethe selected ECG template to the patient ECG signal of the patient bydetermining deviations in the PQRST points of the patient ECG signal andthe template. The cardiac event detector may identify one or morecardiac events based on the deviations. For example, the cardiac eventdetector may determine that the T wave of the patient's ECG signal isinverted relative to the ECG template and the QRS wave of the patient'sECG is wider relative to the ECG template. In this example, the cardiacevent detector may identify these deviations as an occurrence ofpremature ventricular contraction (PVC). It is appreciated that othercardiac events may be detected based on the deviations of the patientECG signal.

In some examples where the medical device is capable of providingtherapy to the patient, the cardiac event detector may perform act 808and provide therapy to the patient. In act 808, the cardiac eventdetector may only provide treatment to the patient if a treatablecardiac event is detected and may withhold treatment to the patient ifan untreatable arrhythmia is detected. Various alarms may be provided tothe patient during the therapy administration process as described inU.S. Patent Publication No. 2015/0039053, titled “SYSTEMS AND METHODS OFDELIVERY THERAPY USING AN AMBULATORY MEDICAL DEVICE” filed on Jun. 27,2014, which is hereby incorporated herein by reference in its entirety.

FIG. 9 illustrates an example ECG template selection process 900performed by, for example, a cardiac event detector such as the cardiacevent detector 424. In one example, the cardiac event detector, whenexecuting the ECG template selection process 900, selects an appropriatetemplate based on the state of the patient. For example, the cardiacevent detector executing the template selection process 900 maydetermine that the patient is active (e.g., exercising) and select anECG template associated with active state of the patient.

As illustrated in FIG. 9, the template selection process 900 includesacts of receiving patient information 902, determining a current patientstate 904, and selecting an ECG template associated with the patientstate 906.

In act 902, the cardiac event detector receives patient information. Thepatient information may include, for example, motion information from anaccelerometer included in or operatively connected to the medicaldevice. For example, such motion information can be used in the next act(act 904) to determine an activity level of the patient.

In act 904, the cardiac event detector determines the current state ofthe patient. For example, the cardiac event detector may determine thatthe patient is in an active state (e.g., exercising) or a resting state(e.g., sitting) based on the motion information. The cardiac eventdetector may determine the state based on the motion information bymonitoring the amount of exercise the patient performed within apredetermined period of time and assigning an activity score to thepatient based on the amount of exercise.

In act 906, the cardiac event detector selects an ECG templateassociated with the current state of the patient. For example, thecardiac event detector may determine that the patient is in an activestate in act 904 (e.g., by noting that the activity score has exceeded athreshold activity score) and select the ECG template associated withthe active state. For example, the threshold activity score can be aparameter than can be predetermined and set by a caregiver or atechnician. The cardiac event detector may also compare the activityscore generated in act 904 with one or more activity scores associatedwith each ECG template and select the ECG template with the closestactivity score.

In other examples, a detector can average in real-time ECG data points(e.g., corresponding to the PQ, QRS, and ST segments) over apredetermined period of time to build an ECG composite. The detector canthen compare each averaged point in the ECG composite with acorresponding point in the current ECG template and calculate acorresponding error value. The detector may perform a similar comparisonwith other ECG templates stored in device memory. The detector can thenselect an ECG template associated with the lowest error value (e.g.,based on a lowest mean error rate). It should be understood that anytechnique for calculating an average deviation from the ECG templatecoefficients may be used to determine an appropriate ECG template to usefor real-time monitoring.

In some situations, before using a selected ECG template, the device canalert and/or upload to a central server the selected ECG template forreview and approval by the patient's caregiver. For example, when thedevice determines that a new template is needed for the patient based,for example, on detecting a deviation above a certain threshold (e.g.,more than 5-10% difference in magnitude comparison and/or phasecomparison), the device can alert the patient's caregiver. The caregivercan then either be prompted to review and approve a new ECG template, orbe provided an ability to re-baseline the patient. For example, thedevice can provide the caregiver an ability to re-baseline the patientremotely without requiring the patient to return to the caregiver'soffice.

FIG. 10 illustrates another example template selection process 1000performed by, for example, a cardiac event detector such as the cardiacevent detector 424. In one example, the cardiac event detector, whenexecuting the template selection process 1000, compares multiple ECGtemplates to select an appropriate template. For example, if there is asubstantial deviation between the initial and subsequent ECG templates,then each template can be evaluated against the incoming ECG signal fordetermining which of the templates may be a better fit to the patientECG information. As noted above, the various ECG templates may be ECGtemplates generated for the same patient at different times to trackchanges in the normal sinus rhythm of the patient.

The template selection process 1000 can include the acts of comparingthe initial ECG template with a subsequent ECG template 1002,determining whether there is a substantial deviation between thetemplates 1004, selecting an initial ECG template 1006, and selecting anECG template with a better fit to the patient ECG information 1008.

In act 1002, the cardiac event detector compares the initial ECGtemplate with a subsequent (e.g., a new or a proposed) ECG template. TheECG templates may be templates formed by the baseline generator 422based on ECG signals from the patient at different times (e.g., 2 weeksapart). As is appreciated by a person of ordinary skill in the art,given the benefit of this disclosure, various methods may be employed tocompare ECG templates. For example, the matched filter coefficients,frequency response, and/or impulse response associated with the matchedfilters of the ECG templates may be compared. In another example, thecardiac event detector may filter the ECG signal of the patient with thematched filters from the respective ECG templates and compare the ECGtemplates by comparing the filtered ECG signal. In act 1004, the cardiacevent detector determines whether there is a substantial deviationbetween the two ECG templates. Various methods may be employed todetermine the similarity between the two templates. For example, thedifference between the matched filter coefficients, frequency response,and/or impulse response of the matched filters associated with therespective ECG templates may be compared with one or more thresholds. Inone example, the matched filter coefficients of each template may beaveraged and a difference between the averages from each template may becompared with a threshold. In another example, the cardiac eventdetector filters the ECG signal of the patient with the matched filtersof the respective ECG templates and assigns a quality score to eachtemplate based on the correlation values output by the matched filters.In this example, the difference between the quality scores associatedwith the respective ECG templates may be compared with a threshold. Thethreshold difference between the ECG templates may be generated by thecardiac detector based on, for example, a maximum rate of change ofnormal human sinus rhythms.

For example, the detector may compare two ECG templates by calculating aseries of error values corresponding to the individual templatecoefficients. Then, the detector can determine if a measure of the errorvalues exceeds a predetermined threshold, e.g., by calculating an rootmean square (RMS) average of the determined error scores and determiningif there is more than, e.g., a 10-20% deviation between a current ECGtemplate and a proposed ECG template to replace the current ECGtemplate. It should be understood that any other technique forcalculating an average deviation of the patient ECG information from theECG template coefficients may be used.

If the cardiac event detector determines that the two templates aresubstantially different, the cardiac event detector proceeds to act 1006and selects the initial ECG template. Selecting the initial template inact 1006 may also include deleting the subsequent ECG template and/orreplacing the initial template with the subsequent ECG template.Otherwise the cardiac event detector proceeds to act 1008 and selectsthe ECG template with the best fit to the ECG signal of the patient.

In act 1008, the cardiac event detector selects the ECG template withthe best fit to the ECG signal of the patient. Various methods may beemployed to compare the ECG signal of the patient with the ECGtemplates. For example, the cardiac event detector may filter the ECGsignal of the patient with one or more matched filters from each ECGtemplate and determine a quality score representative of the matchquality between the matched filter and the ECG signal. The quality scoremay be generated based on the correlations values output by the matchedfilters filtering the ECG signal of the patient. The cardiac eventdetector may select the ECG template associated with the matched filterthat yielded the highest quality score. By way of example, a measure ofa deviation from zero phase crossing and/or magnitude threshold forcurrent patient ECG information can be used as a quality score for aparticular ECG template.

Example Mode Selector

Returning to FIG. 4, the mode selector 420 controls the operating modeof the medical device. For example, the mode selector 420 may determinewhether the medical device operates in a baselining mode or a monitoringmode. The mode selector 420 may select the current operating mode on avariety of parameters. For example, the mode selector 420 may select thecurrent operating mode based on a configurable parameter received froman external entity (e.g., the patient). In addition, the mode selector420 may automatically enter baselining mode on a periodic or aperiodicschedule. Accordingly, the particular criteria employed by the modeselector 420 to determine the operating mode may vary based on theparticular implementation of the medical device.

FIG. 11 illustrates an example mode selection process 1100 performed by,for example, a mode selector such as the mode selector 420. The modeselector 420 may execute the mode selection process 1100 upon a medicaldevice being turned on to identify an appropriate mode for the medicaldevice to initially employ. The mode selection process 1100 includesacts of identifying ECG templates stored in memory 1102, determiningwhether any ECG templates are stored in memory 1104, determining whethernew ECG templates are needed 1106, entering baselining mode 1108, andentering monitoring mode 1110.

In act 1102, the mode selector identifies any ECG templates stored inmemory. The ECG templates may be stored in, for example, the patientdata 416.

In act 1104, the mode selector determines whether any ECG templates arestored in memory. If no ECG templates are stored in memory, the modeselector proceeds to act 1108 and enters baselining mode. Otherwise, themode selector proceeds to act 1106 and determines whether new ECGtemplates are needed.

In act 1106, the mode selector determines whether new ECG templates areneeded based on one or more criteria. For example, the mode selector mayidentify a creation date for any ECG templates stored in the memorydetermine that a new ECG template is needed because the stored ECGtemplates are older than a predetermined value (e.g., older than 2weeks). If the mode selector determines that a new ECG template isneeded, the mode selector proceeds to act 1108 and enters baseliningmode. Otherwise, the mode selector proceeds to act 1110 and entersmonitoring mode.

In some examples, the mode selector may determine that a new ECGtemplate is needed in act 1106 based on a number of false positivearrhythmia detections and/or a number of confirmed arrhythmiadetections. The detected arrhythmias may be confirmed by analyzing thepatient movement, as sensed by a motion detector for example, duringperiods in which an arrhythmia is detected. During an arrhythmia, thepatient likely has irregular bodily movements due to, for example, thepatient falling and/or becoming unconscious. Accordingly, in someexamples, a false positive arrhythmia may be identified by detectingregular patient movement (e.g., the patient is walking normally) duringa period in which an arrhythmia is detected. A confirmed arrhythmia maybe identified by detecting irregular patient movement (e.g., the patientfell) during a period in which an arrhythmia is detected. In addition,arrhythmias may also be confirmed based on user interaction with themedical device after an arrhythmia is detected. For example, the medicaldevice, in some examples, may include one or more buttons operable bythe patient to delay the administration of therapy and/or silence analarm (e.g., response buttons 210 illustrated above in FIG. 2). In thisexample, the medical device may determine that the detected arrhythmiawas a false positive when user interaction with the one or more buttonsis detected. The mode selector may compare the number of confirmedarrhythmia detections and/or the number of false positive arrhythmiadetections with a threshold specified by a configurable parameter todetermine whether a new template is needed. For example, the modeselector may automatically identify that a new template is needed aftertwo false positive arrhythmia detections. In another example, the modeselector may subtract the number of false positive arrhythmia detectionsfrom the number of confirmed arrhythmia detections and compare thedifference with a threshold.

Having thus described several aspects of at least one example of thisdisclosure, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the scope of thedisclosure. Accordingly, the foregoing description and drawings are byway of example only.

What is claimed is:
 1. A medical device to monitor and treat a patientcomprising: at least one electrocardiogram (ECG) sensing electrodeconfigured to sense an ECG signal of the patient; a plurality of therapyelectrodes configured to deliver one or more therapeutic shocks to abody of the patient; and a controller coupled to the at least one ECGsensing electrode and the plurality of therapy electrodes, thecontroller configured to: select a first ECG template of the patientbased on a first ECG signal received during a first period of time;select a second ECG template of the patient different from the first ECGtemplate based on determining from a second ECG signal received from thepatient during a second period of time that the second ECG template ofthe patient represents a better fit for the second ECG signal than thefirst ECG template; determine whether the patient is experiencing atreatable cardiac event during real time monitoring of the patient basedin part on one or more morphological differences between the second ECGsignal in real time and one or more of the first ECG template and thesecond ECG template of the patient; and cause the medical device toinitiate a treatment sequence culminating in the delivery of the one ormore therapeutic shocks to the body of the patient in response todetermining that the patient is experiencing the treatable cardiacevent.
 2. The device of claim 1, wherein the controller is configured totransmit information to a remote system regarding the first ECG templateand the second ECG template.
 3. The device of claim 2, wherein thecontroller is configured to receive approval from the remote system touse one or more of the first ECG template and the second ECG template todetermine whether the patient is experiencing the cardiac event.
 4. Themedical device of claim 1, wherein the selection of the second ECGtemplate by the controller comprises: filtration of the second ECGsignal by the controller through a first matched filter associated withthe first ECG template to generate a first filtered ECG signal;determination by the controller of a first correlation between the firstfiltered ECG signal and the first ECG template; filtration of the secondECG signal by the controller through a second matched filter associatedwith the second ECG template to generate a second filtered ECG signal;determination by the controller of a second correlation between thesecond filtered ECG signal and the second ECG template; and responsiveto the second correlation being higher than the first correlation,selection of the second ECG template.
 5. The medical device of claim 1,wherein the determination whether the patient is experiencing atreatable cardiac event by the controller comprises execution of aconvolution operation on the second ECG signal and at least one of thefirst and second ECG templates to determine whether one or morecharacteristics of the ECG signal indicate either the presence orabsence of the cardiac event.
 6. The medical device of claim 1, whereinat least one of the first and the second ECG signals is received duringoperation of one of a baselining mode and a monitoring mode of themedical device.
 7. The medical device of claim 1, wherein the controlleris configured to generate the second ECG template on a predeterminedschedule.
 8. The medical device of claim 1, wherein the controller isconfigured to generate the second ECG template during a baseliningoperation initiated by one of a remote server, a human operator, and thepatient.
 9. The medical device of claim 1, wherein the controller isconfigured to generate the second ECG template responsive to detectingat least one of a change in patient profile information, a deviceself-test event, a device impact event, a device tampering event, anexcess temperature event, an excess moisture event, a battery changeevent, an arrhythmia warning or alert, an actuation of a response buttonof the medical device, and an error condition of the medical device. 10.The medical device of claim 1, wherein the controller is configured toprovide a notification prior to generating at least one of the first ECGtemplate and the second ECG template.
 11. The medical device of claim 1,further comprising at least one antenna coupled to the controller andwherein the controller is configured to transmit, via the at least oneantenna, one or more of the first ECG template and the second ECGtemplate to an external system.
 12. The medical device of claim 1,further comprising at least one antenna coupled to the controller andwherein the controller is configured to receive, from an external systemvia the at least one antenna, one or more of the first ECG template andthe second ECG template.
 13. A medical device to monitor a patientcomprising: at least one electrocardiogram (ECG) sensing electrodeconfigured to sense an ECG signal of a patient; and a controller coupledto the at least one ECG sensing electrode, the controller configured to:select a first ECG template of the patient based on a first ECG signalreceived during a first period of time; select a second ECG template ofthe patient different from the first ECG template based on determiningfrom a second ECG signal received from the patient during a secondperiod of time that the second ECG template of the patient represents abetter fit for the second ECG signal than the first ECG template; anddetermine whether the patient is experiencing a cardiac event duringreal time monitoring of the patient based in part on one or moremorphological differences between the second ECG signal in real time andone or more of the first ECG template and the second ECG template of thepatient.
 14. The medical device of claim 13, wherein the controller isconfigured to transmit information to a remote system regarding thefirst ECG template and the second ECG template.
 15. The medical deviceof claim 14, wherein the controller is configured to receive approvalfrom the remote system to use one or more of the first ECG template andthe second ECG template to determine whether the patient is experiencingthe cardiac event.
 16. The medical device of claim 13, wherein thecontroller is configured to perform a convolution operation on thesecond ECG signal and at least one of the first and second ECG templatesto determine whether one or more characteristics of the ECG signalindicate either the presence or absence of the cardiac event.
 17. Themedical device of claim 13, wherein at least one of the first and thesecond ECG signals is received during operation of one of a baseliningmode and a monitoring mode of the medical device.
 18. The medical deviceof claim 13, wherein the controller is configured to generate the secondECG template on a predetermined schedule.
 19. The medical device ofclaim 1, wherein the controller is configured to generate the second ECGtemplate during a baselining operation initiated by one of a remoteserver, a human operator, and the patient.
 20. A medical devicecomprising: at least one electrode to sense an electrocardiogram (ECG)signal of a patient; and a controller coupled to the at least oneelectrode, the controller being configured to: generate a first ECGtemplate based on a first ECG signal of the patient; generate a secondECG template based on a second ECG signal of the patient; compare thefirst ECG template to a third ECG signal of the patient; compare thesecond ECG template to the third ECG signal of the patient; select oneof the first ECG template and the second ECG template based on itsrespective comparison to the third ECG signal of the patient; anddetermine whether the patient is experiencing a cardiac event based onthe third ECG signal of the patient and the selected one of the firstECG template and the second ECG template.
 21. The medical device ofclaim 20, wherein the controller is configured to transmit informationto a remote system regarding the first ECG template and the second ECGtemplate.
 22. The medical device of claim 21, wherein the controller isconfigured to receive approval from the remote system to use one or moreof the first ECG template and the second ECG template to determinewhether the patient is experiencing the cardiac event.
 23. The medicaldevice of claim 20, wherein at least one of the first and the second ECGsignals is received during operation of one of a baselining mode and amonitoring mode of the medical device.